Heavy duty radial tire

ABSTRACT

In a heavy duty radial tire, a reinforcement belt  8  outward in a radial direction of the tire and a high-strength belt  13  inward in the radial direction are arranged between a radial carcass  2  and a tread rubber  4 , and an intersect angle between cord  6   a  of an innermost wide-width slant cord layer  6  in the reinforcement belt  8  and cord  12   a  of an outermost narrow-width slant cord layer  12  in the high-strength belt  13  is not less than 10° at an acute angle side, and narrow-width slant cord layers  11, 12  of the high-strength belt  13  in the tire mounted onto a rim and inflated under a maximum air pressure have a width corresponding to 20˜60% of a ground contact width of the tread rubber  4 , and inclination angles of cords  11   a   , 12   a  with respect to an equatorial plane  5  of the tire are not more than 15°, and a rubber gauge t 1  of a first rubber layer  14  between cord  6   a  of an innermost wide-width slant cord layer  6  and cord  12   a  of an outermost narrow-width slant cord layer  12  is 0.9˜3.0 times a cord diameter D of the slant cord layer  11, 12.

TECHNICAL FIELD

This invention relates to a heavy duty pneumatic radial tire used undera higher pressure and a higher load and suitable for constructionvehicles mainly running on rough road, and more particularly to a heavyduty pneumatic radial tire capable of more improving the durability ofthe belt structure by arranging a high-strength belt comprised of atleast one narrow-width slant cord layer between a crown portion of theknown radial carcass and the known reinforcement belt for mitigating anaction of a pressure applied from the radial carcass to the reinforcingbelt accompanied with the expansion of the tire inflated under an airpressure.

BACKGROUND ART

The radial tire has a reinforcement belt comprised of wide-widthrubberized slant cord layers for reinforcing a tread portion between acrown portion of a radial carcass and a tread rubber and developingso-called hoop effect and the like. And also, an inclination angle ofthe cord in each wide-width slant cord layer constituting thereinforcement belt with respect to an equatorial plane of the tire isusually set to be within a range of 20˜40° for causing so-calledpantograph deformation between ply cords of the radial carcass in aproduct tire followed by size growth in vulcanization building or thelike to develop the reinforcing effect and the like. Furthermore, it iscommon that at least two layers among the wide-width slant cord layersare so-called cross cord layers cords of these layers are crossed toeach other with respect to the equatorial plane of the tire.

When an internal pressure is applied to the tire having the above beltstructure by filling an air pressure, the radial carcass indicates atendency of approaching to a circular contour at its section at a stateof arranging no reinforcing belt or at a non-hooped state.

However, since the tire is hooped with the reinforcement belt, thesection of the crown portion in the radial carcass at the inflationunder the internal pressure has actually a radius of curvature largerthan a radius of curvature in the circle. This is simply that thereinforcement belt controls the deformation in a direction of decreasingthe radius of curvature for approaching to the circle or in a directionof growing the size at the tire section. Particularly, a pressure isapplied to a widthwise central portion of the reinforcement beltaccompanied with a force of increasing the carcass size. On the otherhand, both widthwise end portions of the reinforcement belt indicate atendency of separating outward from the radial carcass in the radialdirection of the tire. In case of the tire having such both end portionsof the reinforcement belt, the belt durability in the tire tends to bedegrade by repeatedly subjecting the tire to a large deformation duringthe running under a load. This tendency becomes particularly remarkablein heavy duty radial tires used under a higher internal pressure and ahigher load.

In JP-B-3-23361, JP-B-3-23362 and the like is disclosed, for example,that it is useful to apply a laminate of two narrow-width slant cordlayers, cords of which layers being crossed with each other with respectto the equatorial plane of the tire between the crown portion of theradial carcass and the reinforcement belt as means for mitigating theaction of the pressure applied from the radial carcass accompanied withthe increase of tire size at the inflation under the internal pressureto the reinforcement belt and to arrange a high-strength belt whereinthe inclination angle of these laminated cords with respect to theequatorial plane of the tire is made smaller than the inclination angleof the cord in the wide-width slant cord layers constituting thereinforcement belt in view of the prevention of degrading the beltdurability.

Since the reinforcement belt elongates through shearing deformation at aground contact surface of the tire during the running under a load owingto its properties, there is usually a tendency of creating strainbetween the wide-width slant cord layers constituting the reinforcementbelt due to these shearing deformation and elongation to causeseparation failure. The inventor has examined the belt durability in thetire having the belt structure disclosed in the above publications andelucidated that the tire having such a belt structure controlsseparation failure between the wide-width slant cord layers but tends toeasily cause separation failure between the high-strength belt and thereinforcement belt, and particularly that when the difference of theinclination angle between the cord in the innermost wide-width slantcord layer constituting the reinforcement belt and the cord in theoutermost narrow-width slant cord layer constituting the high-strengthbelt is not less than 10°, separation failure is apt to be remarkablycaused between the high-strength belt and the reinforcement belt and thecord in either one of the innermost slant cord layer and the outermostslant cord layer is apt to be broken in the worst case.

For this end, the inventor has further made various studies in order toprevent the occurrence of separation failure between the high-strengthbelt and the reinforcement belt and found that the occurrence ofseparation failure between the high-strength belt and the reinforcementbelt can effectively be prevented by rationalizing a gauge of rubberlocated between the cord in the innermost wide-width slant cord layerconstituting the reinforcement belt and the cord in the outermostnarrow-width slant cord layer constituting the high-strength belt.

And also, it has been elucidated that the problem similar to thatbetween the high-strength belt and the reinforcement belt may be causedeven between the innermost narrow-width slant cord layer constitutingthe high-strength belt and the carcass ply. Even in this case, it hasbeen found that the occurrence of separation failure between thehigh-strength belt and the carcass ply can effectively be prevented byrationalizing a gauge of rubber located between the innermostnarrow-width slant cord layer constituting the high-strength belt andthe ply cord constituting the radial carcass.

It is, therefore, an object of the invention to provide a heavy dutyradial tire used under a higher pressure and a higher load and suitablefor construction vehicles mainly running on rough road whereinseparation failure apt to be caused between high-strength belt andreinforcement belt is effectively prevented to improve belt durabilityby arranging a high-strength belt between a crown portion of a radialcarcass and a reinforcement belt and rationalizing a gauge of rubberlocated between cord in an outermost narrow-width slant cord layerconstituting the high-strength belt and cord in an innermost wide-widthslant cord layer constituting the reinforcement belt.

DISCLOSURE OF THE INVENTION

In order to achieve the above object, the invention lies in a heavy dutyradial tire comprising a radial carcass toroidally extending between apair of bead cores embedded in respective bead portions, a tread rubber,a reinforcement belt comprised of at least one wide-width rubberizedslant cord layer containing cords arranged obliquely with respect to anequatorial plane and a high-strength belt located inside thereinforcement belt in a radial direction of the tire and comprised of atleast one narrow-width rubberized slant cord layer containing cordsarranged obliquely with respect to the equatorial plane of the tirewherein the reinforcement belt and the high-strength belt are arrangedbetween a crown portion of the radial carcass and the tread rubber andan intersect angle between cord in an innermost wide-width slant cordlayer constituting the reinforcement belt and cord in an outermostnarrow-width slant cord layer constituting the high-strength belt is notless than 10° as measured at an acute angle side, characterized in thatin a widthwise section of the tire when the tire is mounted onto anapproved rim and inflated under a maximum air pressure corresponding toa maximum load capacity, the narrow-width slant cord layer constitutingthe high-strength belt has a width corresponding to 20˜60% of a groundcontact width of the tread rubber and an inclination cord angle of notmore than 15° with respect to the equatorial plane of the tire, and arubber gauge of a first rubber layer located between the cord in theoutermost wide-width slant cord layer and the cord in the innermostnarrow-width slant cord layer is within a range of 0.9˜3.0 times adiameter of the cord in the narrow-width slant cord layer.

The term “approved rim” used herein means an applied rim in a kind oftires, tire size and ply rating described in the following standard(“Approved Rim”, “Recommended Rim”), and the maximum load capacity andmaximum air pressure adopt values described in the following standard.

That is, the standard is decided by an industrial standard effective ina zone manufacturing or using tires, which is, for example, “1999 YearBook” of “The Tire and Rim Association Inc.” in USA, “Standard Manual1999” of “The European Tire and Rim Technical Organization” in Europe,and “JATMA Year Book 1999” of “The Japan Automobile Tire ManufacturersAssociation Inc.” in Japan.

Further, the term “wide-width slant cord layer” used herein concretelymeans a slant cord layer having a width corresponding to 65˜85% of aground contact width of the tread rubber.

Moreover, the term “ground contact width of tread rubber” used hereinmeans a length of a line segment when the tire is mounted onto theapproved rim and inflated under the maximum air pressure correspondingto the maximum load capacity and placed on a flat plate at a staticstate to determine ground contact end positions under a maximum loadcorresponding to the maximum load capacity and the ground contact endpositions are connected along an axial direction of the tire at a stateof turning no load.

Preferably, the high-strength belt has a lamination structure of twonarrow-width slant cord layers, the cords of which layers being crossedwith each other with respect to the equatorial plane, or is comprised ofa single narrow-width slant cord layer.

And also, a rubber gauge of a second rubber layer located between plycord located in the crown portion of the radial carcass and cord in theinnermost narrow-width slant cord layer constituting the high-strengthbelt is within a range of 1.3˜5.0 times a diameter of a cord in thenarrow-width slant cord layer. In this way, the occurrence of separationfailure between the radial carcass and the high-strength belt can moreeffectively be prevented to more improve the belt durability.

Moreover, the rubber gauges of the first rubber layer and the secondrubber layer take values measured at the position on the equatorialplane of the tire.

In addition, it is preferable that the reinforcement belt has a crosscord layer comprised of two wide-width slant cord layers, the cords ofwhich layers being crossed with each other with respect to theequatorial plane of the tire, that an inclination cord angle in thewide-width slant cord layers constituting the cross cord layer withrespect to the equatorial plane of the tire is within a range of 10˜40°,that rubber in the first rubber layer and the second rubber layer has atensile stress at 100% elongation of 2.5˜7.5 MPa, and that a protectionlayer comprised of a rubberized layer containing high-extensible cordsarranged at an inclination angle of 15˜40° with respect to theequatorial plane of the tire is arranged between the tread rubber andthe reinforcement belt so as to cover the full surface of thereinforcement belt.

Moreover, the “tensile stress at 100% elongation” is measured at roomtemperature according to a definition of JIS K6301.

BEST MODE FOR CARRYING OUT THE INVENTION

A best mode for carrying out the invention will be described in detailwith reference to FIG. 1 below.

FIG. 1 is a left-half section view of a main part of a crown portion ofthe heavy duty radial tire according to the invention.

In FIG. 1, numeral 1 is a heavy duty radial tire (hereinafter referredto as a tire), numeral 2 a radial carcass of one ply, numeral 3 a crownportion of the radial carcass 2, numeral 4 a tread rubber, numeral 5 anequatorial plane, numeral 8 a reinforcement belt, and numeral 13 ahigh-strength belt.

The tire 1 comprises the radial carcass 2 toroidally extending between apair of bead cores (not shown) embedded in respective bead portions (notshown). And also, the tire 1 has the reinforcement belt 8 comprised ofat least one layer, two wide-width rubberized slant cord layers 6, 7 inthe illustrated embodiment, and the high-strength belt 13 located insidethe reinforcement belt 8 in the radial direction and comprised of atleast one layer, two narrow-width rubberized slant cord layers 11, 12 inthe illustrated embodiment between the crown portion 3 of the radialcarcass 2 and the tread rubber 4. Each of the slant cord layers 6, 7 andthe slant cord layers 11, 12 has a lamination structure. The slant cordlayers 6, 7 form a cross cord layer wherein cords 6 a, 7 a are extendedobliquely with respect to the equatorial plane 5 of the tire and crossedwith each other with respect to the equatorial plane 5 of the tire. Andalso, the slant cord layers 11, 12 form a cross cord layer wherein cords11 a, 12 a are extended obliquely with respect to the equatorial plane 5of the tire and crossed with each other with respect to the equatorialplane 5 of the tire. Particularly, an intersect angle between the cord 6a in the innermost wide-width slant cord layer 6 constituting thereinforcement belt 8 and the cord 12 a in the outermost narrow-widthslant cord layer 12 constituting the high-strength belt 13 is not lessthan 10° as measured at an acute angle side.

The reason why the intersect angle is restricted to not less than 10° isdue to the fact that when it is less than 10°, a tension bearing ratioof the high-strength belt 13 decreases and tension corresponding to thedecreased portion of the tension bearing ratio is applied to thereinforcement belt 8 and hence the separation resistance of thereinforcement belt 8 lowers. Although the occurrence of separationbetween the reinforcement belt 8 and the high-strength belt 13 becomesremarkable when the intersect angle is not less than 10° in theconventional tire, the invention is to effectively control theoccurrence of separation failure between the reinforcement belt 8 andthe high-strength belt 13.

Moreover, the high-strength belt 13 has a belt structure providing ahighest rigidity among the existing belts and is enough to be comprisedof one or two narrow-width slant cord layers. For example, when thehigh-strength belt 13 is comprised of three or more narrow-width slantcord layers, the rigidity too rises and there is a fear of lowering theenveloping property and the like and also there is caused aninconvenience that strain at an end portion of the high-strength belt 13becomes large. In the present tires, particularly heavy duty tires,therefore, the number of the narrow-width slant cord layers constitutingthe high-strength belt is adaptable to be one or tow. For convenience'sake, the cords 6 a, 7 a, 11 a, 12 a of the slant cord layers 6, 7, 11,12 are schematically shown by an oblong shape in FIG. 1.

A primary characteristic of the invention lies in that in a widthwisesection of the tire 1 when the tire 1 is mounted onto an approved rim toform a tire-rim assembly and inflated under a maximum air pressurecorresponding to a maximum load capacity, each of the narrow-width slantcord layers 11, 12 constituting the high-strength belt 13 has a widthcorresponding to 20˜60% of a ground contact width of the tread rubber 4,and an inclination cord angle of the cords 11 a, 12 a with respect tothe equatorial plane 5 of the tire is not more than 15°, and a rubbergauge t₁ of the first rubber layer 14 located between the cord 6 a inthe outermost wide-width slant cord layer 6 and the cord 12 a in theinnermost narrow-width slant cord layer 12 is within a range of 0.9˜3.0times a diameter D (mm) of the cord 11 a, 12 a in the narrow-width slantcord layer 11, 12. By rationalizing the rubber gauge t₁ of the firstrubber layer 14 can effectively be controlled the occurrence ofseparation failure apt to be caused between the reinforcement belt 8 andthe high-strength belt 13. The approved rim, maximum load capacity andmaximum air pressure are according to the above standard and also theground contact width is according to the above definition.

Moreover, the reason why the rubber gauge t₁ of the first rubber layer14 is restricted to a range of 0.9˜3.0 times the diameter D of the cord11 a, 12 a of narrow-width slant cord layer 11, 12 is as follows. Thatis, when the rubber gauge t₁ of the first rubber layer 14 is less than0.9×D (mm), the rubber gauge of the first rubber layer 14 becomes toothin and the cord 6 a in the innermost wide-width slant cord layer 6constituting the reinforcement belt 8 is close to the cord 12 a in theoutermost narrow-width slant cord layer 12 constituting thehigh-strength belt 13 and hence shearing strain produced between theselayers can not effectively be reduced and the occurrence of separationfailure can not sufficiently be prevented. On the other hand, when therubber gauge t₁ (mm) of the first rubber layer 14 exceeds 3.0×D (mm),the rubber gauge of the first rubber layer 14 becomes too thick and theeffect as the reinforcement belt 8, concretely hoop effect of the crosscord layer in the size growth of the tire 1 when the reinforcement belt8 has a cross cord layer structure can not sufficiently be developed. Inother words, the rigidity of the reinforcement belt 8 extremely lowersand the effect of controlling the size growth is degraded.

And also, the reason why the width of the narrow-width slant cord layer11, 12 is restricted to a range of 20˜60% of the ground contact width ofthe tread rubber 4 is due to the fact that when the width of thenarrow-width slant cord layer 11, 12 exceeds 60% of the ground contactwidth, strain at the end portion of the slant cord layer 11, 12violently increases, while when it is less than 20% of the groundcontact width, pressure applied from the radial carcass 2 to thereinforcement belt 8 in the inflation of the tire 1 under the internalpressure can not sufficiently be decreased.

Further, the reason why the inclination angle of the cord 11 a, 12 a inthe narrow-width slant cord layer 11, 12 is restricted to not more than15° is due to the fact that when the inclination angle exceeds 15°, thehoop effect is insufficient and pressure applied from the radial carcass2 to the reinforcement belt 8 under the inflation of the internalpressure can not sufficiently be decreased.

Moreover, there is a tendency that separation failure is apt to becaused between the radial carcass 2 and the high-strength belt 13 fromthe same reason as in the case between the reinforcement belt 8 and thehigh-strength belt 13.

In addition to this tendency, a problem as shown in FIG. 2 is causedwhen the ply cords 2 a of the radial carcass 2 come extremely close tothe cords 11 a of the innermost narrow-width slant cord layer 11constituting the high-strength belt 13 in the tire production. FIG. 2 isa diagrammatic view illustrating a state of changing the ply cords ofthe radial carcass in the conventional tire into a wavy form accompaniedwith the shearing deformation of the innermost narrow-width slant cordlayer in the vulcanization building of the tire. As shown in FIG. 2, theabove problem means that in the conventional tire, the ply cord 2 a ₁,(shown by a dot-dash line) before the vulcanization building is renderedinto the wavy ply cord 2 a ₂ after the vulcanization building (shown bya solid line). That is, the high-strength belt 13 is required to beenlarged to a certain level from a stage of building an uncured tirewherein an uncured cord layer member is shaped into a ring on a BT drumin an apparatus for previously laying an uncured cord layer member andan uncured tread rubber up to a product tire. In this case, the belt isstretched by shearing deformation at the vulcanization building. The plycord 2 a ₁ is drawn by the shearing deformation of the cord 11 a in theinnermost narrow-width slant cord layer 11 constituting thehigh-strength belt 13 and tends to deform into the wavy ply cord 2 a ₂.This phenomenon remarkably appears when the enlargement ratio of thehigh-strength belt 13 is not less than 5% and the inclination angle ofthe cord 11 a in the innermost narrow-width slant cord layer 11 withrespect to the equatorial plane 5 of the tire is not more than 15°. Sucha wavy ply cord 2 a ₂ is unfavorable because compression strain islocally applied during the running of the tire 1 under a load.

Therefore, it is necessary to effectively prevent the occurrence ofseparation failure between the radial carcass 2 and the high-strengthbelt 13 and at the same time prevent the change of the ply cord 2 a intothe wavy form. For this end, it is favorable that a rubber gauge t₂ (mm)of a second rubber layer 15 located between ply cord 2 a located in thecrown portion 3 of the radial carcass 2 and cord 11 a in the innermostnarrow-width slant cord layer 11 constituting the high-strength belt 13is within a range of 1.3˜5.0 times a diameter D (mm) of the cord 11 a,12 a in the narrow-width slant cord layer 11, 12. The diameters D (mm)of the cords 11 a, 12 a are the same.

The reason why the rubber gauge t₂ of the second rubber layer 15 isrestricted to a range of 1.3˜5.0 times a diameter D of the cord 11 a, 12a in the narrow-width slant cord layer 11, 12 is as follows. That is,when the rubber gauge t₂ of the second rubber layer 15 is less than1.3×D (mm), the rubber gauge t₂ of the second rubber layer 15 becomestoo thin and hence the shearing strain produced between the radialcarcass 2 and the innermost narrow-width slant cord layer 11constituting the high-strength belt 13 can not be decreased and theoccurrence of separation failure can not sufficiently be prevented. Inaddition, the ply cord 2 a is unfavorably drawn by the deformation ofthe cord 11 a in the innermost narrow-width slant cord layer 11 of thehigh-strength belt 13 to indicate the wavy form in the vulcanizationbuilding.

On the other hand, when the rubber gauge t₂ of the second rubber layer15 exceeds 5.0×D (mm), the rubber gauge t₂ of the second rubber layer 15becomes too thick and hence the effect as the reinforcement belt,concretely hoop effect of the cross cord layer in the size growth of thetire 1 when the reinforcement belt 8 has a cross cord layer structurecan not sufficiently be developed. In other words, the rigidity of thereinforcement belt 8 extremely lowers and the effect of controlling thesize growth is degraded.

Since the tire 1 according to the invention is used under conditions ofhigh internal pressure and high load, as shown in FIG. 1, thereinforcement belt 8 is adaptable to be a cross cord layer comprised oftwo laminated wide-width slant cord layers 6, 7, cords 6 a, 7 a of whichlayers being crossed with each other with respect to the equatorialplane 5 of the tire. In this case, the inclination angles of the cords 6a, 7 a in the wide-width slant cord layers 6, 7 constituting the crosscord layer are adaptable within a range of 10˜40° with respect to theequatorial plane 5 of the tire, respectively. The above range of theinclination angle is effective for preventing the trouble of cut throughthe wide-width slant cord layer 6, 7 because when the tire 1 rides overprojections existing on a road surface such as small stones, rocks andthe like, even if the projection passes through the tread rubber 4 toarrive at the reinforcement belt 8, the wide-width slant cord layer 6, 7has a flexibility.

And also, when it is required to protect the reinforcement belt 8 fromthe projections, it is effective to arrange a protection layer 16 madeof a rubberized layer containing high-extensible cords arranged at aninclination angle of 15˜40° with respect to the equatorial plane Ebetween the tread rubber 4 and the reinforcement belt 8 so as to coverthe full surface of the reinforcement belt 8. As the high-extensiblecord, it is favorable to use cords having, for example, an elongation atbreak of not less than 4%.

Although the first rubber layer 14 and the second rubber layer 15 shownin FIG. 1 are made of rubber other than coating rubber constituting theslant cord layers 6, 7, 11, 12, each of the first rubber layer 14 andthe second rubber layer 15 may be made of only the coating rubberconstituting the slant cord layer 6, 7, 11, 12, so that rubber materialis not particularly restricted. And also, rubber in the first rubberlayer 14 and the second rubber layer 15 is suitable to have a tensilestress at 100% elongation of 2.5˜7.5 MPa.

Although the above shows only an embodiment of the best mode of theinvention, various modifications may be made within the scope of theinvention.

There are prepared six kinds of the tire 1 as an example according tothe invention and the durability thereof is evaluated as follows.

Each tire of Examples 1˜6 is a radial ply tire for construction vehiclehaving a tire size of 37.00R57. The width (mm) of slant cord layers 11,12 constituting the high-strength belt 13 (only one slant cord layer 11in Example 6), inclination angle (°) and diameter D (mm) of cord 11 a,12 a, width (mm) of slant cord layer 6, 7 constituting the reinforcementbelt 8, inclination angle (°) of cord 6 a, 7 a, width (mm) of protectionlayer 16 and inclination cord angle (°) thereof, rubber gauge t₁ (mm) offirst rubber layer 14 and rubber gauge t₂ (mm) of second rubber layer 15are shown in Table 1.

The radial carcass 2 is made of one ply and steel cords are used as aply cord 2 a. The cord diameter is 3.2 mm. The tread rubber 4 has aground contact width of 840 mm. The other tire structure issubstantially the same as that of the conventional radial ply tire forconstruction vehicle according to custom. In order to evaluate the beltdurability level in each example tire, there are prepared a conventionaltire having only the reinforcement belt made of four wide-width slantcord layers without using the high-strength belt 13 and tires ofComparative examples 1˜4 wherein the rubber gauge t1 of the first rubberlayer 14 is outside the adequate range and dimensions of these tires arealso shown in Table 1.

TABLE 1 First Second High-strength belt 13 Reinforcement belt 8Protection rubber rubber innermost layer 11 outermost layer 12 innermost layer 6 outermost layer 7 layer 16 layer 14 layer 15 inclinationinclination cord inclination inclination inclination rubber rubber cordangle cord angle diameter cord angle cord angle cord angle gauge gaugewidth *1 width *1 D width *1 width *1 width *1 t₁ t₂ (mm) (°) (mm) (°)(mm) (mm) (°) (mm) (°) (mm) (°) (mm) (mm) Conventional high-strengthbelt: none, reinforcement belt: 4 layers → innermost layer: width 600mm, R27°, middle lower layer: width 740 mm, Example L25°, middle upperlayer: width 660 mm, R22°, outermost layer: width 500 mm, L22°, corddiameter: 2.8 mm, rubber gauge of first rubber layer: 2.2 mm, rubbergauge of second rubber layer: 3.6 mm, protection layer: width 800 mm,L22° Comparative 380 R5 340 L5 2.8 660 R22 500 L22 800 L22 1.5 3.2Example 1 Comparative 380 R5 340 L5 2.8 660 R22 500 L22 800 L22 1.8 4.5Example 2 Comparative 380 R5 340 L5 2.8 660 R22 500 L22 800 L22 9.0 5.0Example 3 Comparative 440 R5 — — 3.0 660 L20 500 R20 800 R25 1.5 3.5Example 4 Example 1 380 R5 340 L5 2.8 660 R22 500 L22 800 L22 2.9 3.6Example 2 380 R5 340 L5 2.8 660 R22 500 L22 800 L22 2.4 7.5 Example 3380 R5 340 L5 2.8 660 R22 500 L22 800 L22 4.0 8.5 Example 4 220 R7 200L7 2.5 580 L30 450 R25 800 L22 2.5 3.3 Example 5 300  L10 250  R10 3.0600 L30 530 R25 800 L22 9.0 15.0  Example 6 440 R5 — — 3.0 660 L20 500R20 800 R25 3.0 4.8 *1: In the column of inclination cord angle, [R] isupward to the right, and [L] is upward to the left.

The belt durability of each tire is evaluated under the following testconditions. That is, the tire is mounted onto an approved rim (rimcontour: 27.00 inch, rim width: 27.00 inch, rim diameter: 57 inch) andthe tire-rim assembly is inflated under a maximum air pressure of 700kPa and run on a drum rotating at a periphery velocity of 15 km/h at astate of pushing under a load of 51500 kgf corresponding to a maximumload capacity for 300 hours. After the completion of the running, thetire is cut to measure a separation length between the reinforcementbelt 8 and the high-strength belt 13 (crack length) and separationlength between the high-strength belt 13 and the radial carcass 2 (cracklength), whereby the belt durability is evaluated. The measured resultsare shown in Table 2. The numerical values in Table 2 are represented byan index on the basis that the separation length of Comparative Example1 is 100. The smaller the index value, the better the property.

TABLE 2 Separation between Separation between layers *1 layers *2Conventional Example 120 123 Comparative Example 1 100 100 ComparativeExample 2 98 97 Comparative Example 3 97 98 Comparative Example 4 99 99Example 1 81 92 Example 2 95 88 Example 3 86 73 Example 4 73 86 Example5 61 84 Example 6 83 78 *1: Evaluation of separation by crack lengthbetween innermost wide-width slant cord layer 6 and outermostnarrow-width slant cord layer 12. *2: Evaluation of separation by cracklength between innermost narrow-width slant cord layer 11 and carcassply 2.

As seen from the results of Table 2, all tires of Examples 1˜6 areconsiderably excellent in the belt durability as compared with the tireof Comparative Example 1 wherein the rubber gauges of the first rubberlayer 14 and the second rubber layer 15 are outside the adequate ranges.And also, the sufficient belt durability can not be obtained in thetires of Comparative Examples 2˜4 because the rubber gauge t₁ of thefirst rubber layer 14 is outside the adequate range of the invention.

INDUSTRIAL APPLICABILITY

According to the invention, strain between the wide-width slant cordlayers 6 and 7 constituting the reinforcement belt 8 can be decreased byarranging the high-strength belt 3 to prevent the separation failurebetween these layers 6 and 7, and separation failure apt to be causedbetween the high-strength belt 13 and the reinforcement belt 8 caneffectively be prevented by rationalizing the rubber gauge t1 of thefirst rubber layer 14, and consequently there can be provided heavy dutyradial tires having an excellent belt durability, particularly a heavyduty radial tire suitable for use in a construction vehicle mainlyrunning on rough road or the like.

And also, separation failure between the radial carcass 2 and thehigh-strength belt 13 can effectively be prevented and the occurrence ofthe problem causing the wavy formation of the ply cord 2 a can beprevented by rationalizing the rubber gauge t₂ of the second rubberlayer 15 located between the ply located in the crown portion of theradial carcass 2 and the innermost narrow-width slant cord layer 11constituting the high-strength belt 13.

Furthermore, when the reinforcement belt 8 is a cross cord layer, theinclination angles of the cords 6 a, 7 a in the wide-width slant cordlayers 6, 7 constituting the cross cord layer with respect to theequatorial plane 5 of the tire is made to a range of 10˜40°,respectively, so that when the tire rides on projections existing on aroad surface such as small stones, rocks and the like and the projectionpasses through the tread rubber 4 to arrive at the reinforcement belt 8,it is difficult to cause the trouble of cut through the reinforcementbelt 8 because the reinforcement belt 8 has a flexibility, whereby thebelt durability is also improved.

Moreover, the arrival of the projection at the reinforcement belt 8through the tread rubber 4 can effectively be prevented by arranging theprotection layer 16 made of the rubberized layer containinghigh-extensible cords arranged at an inclination angle of 15˜40° withrespect to the equatorial plane of the tire between the tread rubber 4and the reinforcement belt 8 so as to cover the full surface of thereinforcement belt 8.

In addition, each of the first rubber layer 14 and the second rubberlayer 15 is made of rubber having a tensile stress at 100% elongation of2.5˜7.5 MPa, whereby the belt durability can be more improved.

What is claimed is:
 1. A heavy-duty radial tire comprising: a radialcarcass toroidally extending between a pair of bead cores embedded inrespective bead portions; a tread rubber; a reinforcement belt comprisedof at least one wide-width rubberized slant cord layer containing cordsarranged obliquely with respect to an equatorial plane; a high strengthbelt located inside the reinforcement belt in a radial direction of thetire and comprised of at least one narrow-width rubberized slant cordlayer containing cords arranged obliquely with respect to the equatorialplane of the tire, wherein: the reinforcement belt and the high strengthbelt are arranged between a crown portion of the radial carcass and thetread rubber; an intersect angle between a cord in a radially innermostwide-width slant cord layer constituting the reinforcement belt and acord in a radially outermost narrow-width slant cord layer constitutingthe high strength belt is not less than 10° as measured at an acuteangle side; in a widthwise section of the tire when the tire is mountedonto an approved rim and inflated under maximum air pressurecorresponding to a maximum load capacity, the at least one narrow-widthslant cord layer constituting the high strength belt has a widthcorresponding to 20-60% of a ground contact width of the tread rubberand an inclination angle of not more than 15° with respect to theequatorial plane of the tire; a first rubber layer is located betweenthe radially innermost wide-width slant cord layer and the radiallyoutermost narrow-width slant cord layer; and a rubber gauge between thecord in the radially innermost wide-width slant cord layer and the cordin the radially outermost slant cord layer is within a range of 0.9-3.0times a diameter of the cord in the radially outermost narrow-widthslant cord layer.
 2. A heavy duty radial tire according to claim 1,wherein the high-strength belt comprises two narrow-width slant cordlayers laminated one upon the other, the cords of which layers beingcrossed with each other with respect to the equatorial plane.
 3. A heavyduty radial tire according to claim 1, wherein the high-strength belt iscomprised of a single narrow-width slant cord layer.
 4. A heavy dutyradial tire according to claim 1, wherein a rubber gauge of a secondrubber layer located between a ply cord located in the crown portion ofthe radial carcass and a cord in the radially innermost narrow-widthslant cord layer constituting the high-strength belt is within a rangeof 1.3˜5.0 times a diameter of a cord in the radially innermostnarrow-width slant cord layer.
 5. A heavy duty radial tire according toclaim 1, wherein the reinforcement belt has a cross cord layer comprisedof two wide-width slant cord layers, the cords of which layers beingcrossed with each other with respect to the equatorial plane of thetire, and an inclination cord angle in the wide-width slant cord layersconstituting the cross cord layer with respect to the equatorial planeof the tire is within a range of 10˜40°.
 6. A heavy duty radial tireaccording to claim 4, wherein rubber in the first rubber layer and thesecond rubber layer has a tensile stress at 100% elongation of 2.5˜7.5MPa.
 7. A heavy duty radial tire according to claim 1, wherein aprotection layer comprised of a rubberized layer containinghigh-extensible cords arranged at an inclination angle of 15˜40° withrespect to the equatorial plane of the tire is arranged between thetread rubber and the reinforcement belt so as to cover the full surfaceof the reinforcement belt.